Now that NASA's Phoenix Mars Lander is likely dead, mission scientists have time to fully examine the treasure trove of data generated in its five months in the red planet's arctic region, in order to shed more light on the mysteries of Mars.

Phoenix's confirmation of water ice below the Martian arctic surface and its surprising characterization of the Martian dirt are among the findings researchers will be busy investigating further in the next few months.

Beginning to end
Phoenix landed in the Vastitas Borealis plains of Mars on May 25 to the jubilant cheers of mission controllers. (Phoenix was in part a replacement for the failed Mars Polar Lander, so tensions to have a successful landing were running high.)

In the five-plus months it spent alive at its landing site, the spacecraft dug up samples of Martian dirt and subsurface water ice and analyzed them for signs of the planet's past potential habitability.

Yesterday NASA announced that the mission, whose final cost was about $475 million, was effectively over. Dwindling sunlight (caused by the transition from summer to fall at Phoenix's location, which is roughly equivalent to northern Alaska on Earth) and light-obscuring dust in the atmosphere finally pushed Phoenix below its power threshold on Nov. 2.

"It's rather tough living up north above the (Martian) arctic circle, so we always knew that the end would be coming near for us," said Phoenix project manager Barry Goldstein of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Phoenix's demise, while expected to come with diminishing light and plummeting temperatures, occurred a few weeks sooner than engineers had hoped, largely due to the poor weather at its landing site. But even with its early death, Phoenix went above and beyond its primary mission goals, which were achieved by the end of its original three-month mission in August.

"The vehicle ... has achieved all of its science goals and then some, and I've think we have had a huge success," Goldstein said.

The biggest success of the mission was to confirm the presence of water ice under the surface of the Martian arctic — which had first been detected by the Mars Odyssey orbiter in 2002 — though that discovery didn't come right away.

"When we landed, we looked around, we saw a field of dirt and rocks that was spread out to the horizon, and we didn't see ice right away, it wasn't until we looked under the spacecraft that we found out we were standing on it, and this was quite a thrill for everybody," said Phoenix principal investigator Peter Smith of the University of Arizona in Tucson.

Over the course of the mission, Smith and his team used Phoenix's robotic arm and analysis instruments to scrape, poke, prod and characterize this rock-hard ice layer.

"We've excavated to the ice, we know its depth, we know how it changes over the surface, we've seen different types of ice," Smith said, adding that the analysis of the ice isn't over.

In digging down to the subsurface ice layer, Phoenix also scooped up samples of the overlying dirt and analyzed them in its microscopes, wet chemistry lab (which dissolved the samples in water to look for soluble chemicals) and Thermal and Evolved-Gas Analyzer (TEGA) (which baked the samples and analyzed the vapors given off). These analyses led to some surprising findings.

Unlike other landers and rovers that have detected acidic dirt with plenty of sulfates — indicative of volcanic activity — Phoenix found the dirt at its landing site was alkaline with lots of carbonates and clay minerals, the later of which typically form when liquid water is around.

"On the Earth, we would conclude immediately that there was liquid water in this soil — for Mars we have to be a little more careful, and we're going to develop this story as we can, as we interpret our data," Smith said. "But definitely liquid water has been a part of this soil" in the past.

The dirt samples also showed evidence of salts and perchlorate. Perchlorate was "totally unexpected," Smith said, and "has profound implications for Mars," because it can act as a potential energy source for microbes.

Life?
"And that leads to the question, is this a habitable zone? Have we found such a thing on Mars?" Smith said. The analysis the team will carry out now will aim to help answer those questions, he said. Such research could set the stage for future missions that might actually look for biology on the red planet.

Phoenix also took roughly 25,000 pictures during its tenure on Mars, from complete 360-degree panoramas to close-up peeks at the ice in trenches it dug.

The lander also took weather measurements, including pressure, temperature, winds, and humidity.

"We've got a complete weather record for the entire time we were there," Smith said, adding that it was "one of the major accomplishments of the mission."

Towards the end of the mission, the team even saw frost forming on the surface and snow falling from the sky.

"This is really unexpected, and I think a first to see it, especially from the surface," Smith said.

Though mission team members were disappointed by the lander's premature demise, they looked forward to the information it would bring them on Mars.

"While we're losing a spacecraft, it's really an Irish wake rather than a funeral we're looking forward to here," said Dough McCuistion, director of the Mars Exploration Program at NASA Headquarters in Washington, D.C. "We should celebrate what Phoenix has done, what the Phoenix team has done, and where it's going to take us in the future."

Future Mars exploration
Up next for Mars are the planned Mars Science Laboratory mission, currently still slated for a 2009 launch, and the next member of the Scout mission (of which Phoenix was the first) — the MAVEN orbiter.

MAVEN will examine the upper and middle atmosphere of Mars to understand how materials, especially water, escape from the planet's gravitational pull. Understanding this link of Mars' water cycle will help scientists "to understand what the history of liquid water on the surface of Mars may have been in the past," McCuistion said.

Phoenix's success "has really set a standard for future Scout missions," he added.

Even with its success, Phoenix ran into its share of snags. "A lot of lessons [were] learned in this mission," McCuistion said.

The unexpected stickiness of the Martian dirt made it difficult to deliver samples to the lander's instruments, as they would get stuck in openings and to the robotic arm's scoop.

"We learned a lot about handling of soils, soil consistency and how difficult it can be," McCuistion said.

Along those lines, the team learned "how difficult it is to handle ice when it sublimes quickly in the atmosphere," he added.

But overall, NASA was pleased with the Phoenix mission and its accomplishments, as were the members of the team who planned, built, and operated the lander.

"I'm just thrilled to death with what we've been able to do here," Smith said.